Joints often undergo degenerative changes due to a variety of reasons. When degeneration becomes advanced or irreversible it may become necessary to replace a native joint with a prosthetic joint. Degenerative disease or injury may require replacement of all or a portion of a patient's joint using synthetic material, typically metals, ceramics, or polymer materials. Artificial implants, including hip implants, shoulder implants and knee implants made from these materials, are widely used in orthopedic surgery to strengthen or replace degenerating joints.
In a primary replacement surgery, a patient's native joint is replaced with a prosthetic implant. The implant is designed to integrate with the patient's bone and provide the same function and motion as the native joint that is being replaced. After a primary replacement, it may become necessary to conduct a second or subsequent revision surgery in order to replace a prosthetic joint with a replacement joint which is often larger than the primary replacement. Such surgeries often become necessary due to further degeneration of bone or advancement of a degenerative disease requiring replacement of the implant and diseased bone with a larger, enhanced prosthetic joint, often referred to as a revision prosthesis. For example, bone is often lost around the rim of an acetabulum around a hip implant, and thus may provide less rim coverage to securely hold a press-fit acetabular shell. A larger shell can be placed into the acetabulum in a revision surgery to make up for the lost bone.
In both primary and revision replacement surgeries, a patient's native bone may have defects or voids that a surgeon can fill with bone grafts before inserting an implant. This process may be time consuming and expensive and may subject the patient to health risks. In order to facilitate successful implants in a bone having defects or voids, a surgeon may use implant augments in conjunction with standard implant components to fill in the voids. Such augments can be coupled or otherwise attached to an outer surface of an implant in the area of a bone void or defect in the native bone. In addition to primary surgery, augments are often used in revision surgeries due to bone degeneration, bone loss or other defects in the degenerative area that necessitates the revision surgery.
A degree of variability in implant augments may be desired, as the location and nature of the native bone and the bone defects vary from patient to patient. Especially when defects or voids in the bone are present, it is preferable for a surgeon to have the ability to adjust the implant to fit the bone, rather than adjusting the bone to fit a rigid implant. Adjusting the implant or implant augments allows for conservation of native bone rather than requiring reaming or other removal of a patient's native bone in preparation for implant placement. Conserving bone supplements the support that the bone gives to the implant component. Especially in the cases of diseased bone or damaged bone in revision surgery, any bone that is removed to prepare for the implant may prove detrimental to the integrity of the bone and its ability to withstand significant forces following implantation.
To supplement fixation of orthopedic implants into native bone, implants can incorporate mechanical fasteners, such as screws, and locking mechanisms that engage the screws in a locked configuration relative to both the bone and the implant. Such fasteners and locking mechanisms can be used to hold the implant in place and reduce detrimental effects caused by implant movement. While the locking mechanisms provide a steady hold between the fastener and the implant, the nature of the locking mechanisms often limits the orientation in which the fastener can be locked. The locking mechanisms often require that the fastener be inserted in a certain direction along a given axis in order to engage the locking mechanism of the implant.
Implementing locking screws and locking mechanisms into implant augments may be desirable to increase the hold of the implants and augments into native bone. The locking mechanisms may also, however, cut down on variability of augments and the number of orientations in which an augment can be inserted into a bone, given the limited function of the locking mechanisms. Incorporating a locking mechanism into an augment may require a surgeon to choose between placing the augment in an orientation with a strong hold of the locking mechanisms or placing the augment in an orientation that creates better contact with the native bone into which the augment is placed, but creates a weaker engagement of the locking mechanism. This can create problems and result in inadequate fixation of an augment or an undesirable positioning of the augment in native bone.